1. Field of the Invention
The present invention relates generally to the field of display devices. In particular, the present invention relates to an optical system and method for coupling an image onto a display device. More specifically, the present invention relates to an optical system and method for coupling an image onto an ultrathin planar optical display device which is capable of reducing or eliminating distortions that typically occur when an image is projected onto a display device which is tilted in relation to the incident image.
2. Description of the Background
Optical screens typically use cathode ray tubes (CRTs) for projecting images onto the screen. The standard TV screen has a width to height ratio of 4:3 with 525 vertical lines of resolution. An electron beam is scanned both horizontally and vertically across the screen to form a number of pixels which collectively form the image.
Conventional cathode ray tubes have a practical limit in size, and are relatively deep to accommodate the required electron gun. Larger screens are available which typically include various forms of image projection. However, such screens have various viewing shortcomings including limited viewing angle, resolution, brightness, and contrast, and such screens are typically relatively cumbersome in weight and shape. Furthermore, it is desirable for screens of any size to appear black in order to improve viewing contrast. However, it is impossible for direct view CRTs to actually be black because they utilize phosphors to form images, and those phosphors are non-black.
Optical panels may be made by stacking optical waveguides, each waveguide having a first end and a second end, wherein an outlet face is defined by the plurality of first ends, and wherein an inlet face is defined by the plurality of second ends. Such a panel may be thin in its depth compared to its height and width, and the cladding of the waveguides may be made black to increase the black surface area, but such a panel may require expensive and cumbersome projection equipment to distribute the image light across the inlet face, which equipment thereby increases the total size and cost of the panel.
Therefore, the need exists for an optical panel which possesses the advantages corresponding to a stacked waveguide panel, but which does not require the use of expensive and cumbersome projection equipment, nor suffer from the increase in size and cost necessitated by such equipment.
In optical panels where the depth of the housing (containing the optical panel and projection equipment) is desired to be at a minimum, the projection equipment is typically positioned to accommodate these overall dimension constraints. The positioning of the projection equipment may therefore require the image path to be directed at an acute angle with respect to the targeted outlet face of the panel. Thus, since the surface of the outlet face is generally highly tilted relative to the image path, an imaging system which is capable of producing an image which is focused and is without distortions is critical. Not only is a properly focused image desired, but an image produced on the surface of the outlet face must also have little or no chromatic distortion and must retain the desired aspect ratio while maintaining a linear point-to-point mapping of the image.
Therefore, the need also exists for an optical system for an optical panel which is capable of producing an accurate image on a highly tilted inlet face surface relative to the image path, and which does not suffer from improperly focused images and image distortions which yield chromatic distortions, false aspect ratios, and inconsistent, linear point-to-point mapping of the image.
The present invention is directed to an optical system for projecting an image onto a display image plane at an incident angle which is greater than zero. The optical system comprises an image source and an imaging element. The imaging element creates an image from the image source. The optical system also comprises an anamorphic telescope for reducing anamorphic distortion of the image, and a final mirror for reflecting the image toward the display image plane. The anamorphic telescope reduces magnification of the image in a first direction and enlarges magnification of the image in a second direction which is perpendicular to the first direction. Moreover, the anamorphic telescope includes a first lens group, a second lens group, and a third lens group. The first lens group and the second lens group form a first anamorphic telescopic system, and the second lens group and the third lens group form a second anamorphic telescopic system. The anamorphic telescope also may be constructed of more than one optical material to correct chromatic aberrations of the image. The present invention is also directed to a display system which includes the combination of an optical system and an optical panel.
The present invention solves problems experienced in the prior art, such as the use of expensive and cumbersome projection equipment, by providing an optical system having a reduced optical path that produces an accurate image on a highly tilted inlet face surface relative to the image path, and which does not suffer from chromatic distortion, improperly focused images, image distortions which yield false aspect ratios or inconsistent point-to-point mapping to the image. The present invention also retains the advantages which correspond to a stacked waveguide panel, such as improved contrast and minimized depth of the panel and surrounding housing.
Those and other advantages and benefits of the present invention will become apparent from the detailed description of the invention hereinbelow.